date_trunc

Description

Truncates a time value based on the specified date part, such as year, day, hour, or minute.

StarRocks also provides the year, quarter, month, week, day, and hour functions for you to extract the specified date part.

Syntax

DATETIME date_trunc(VARCHAR fmt, DATETIME|DATE datetime)

Parameters

datetime: the time to truncate, which can be of the DATETIME or DATE type. The date and time must exist. Otherwise, NULL will be returned. For example, 2021-02-29 11:12:13 does not exist as a date and NULL will be returned.
fmt: the date part, that is, to which precision datetime will be truncated. The value must be a VARCHAR constant. fmt must be set to a value listed in the following table. If the value is incorrect, an error will be returned.

Value	Description
second	Truncates to the second.
minute	Truncates to the minute. The second part will be zero out.
hour	Truncates to the hour. The minute and second parts will be zero out.
day	Truncates to the day. The time part will be zero out.
week	Truncates to the first date of the week that `datetime` falls in. The time part will be zero out.
month	Truncates to the first date of the month that `datetime` falls in. The time part will be zero out.
quarter	Truncates to the first date of the quarter that `datetime` falls in. The time part will be zero out.
year	Truncates to the first date of the year that `datetime` falls in. The time part will be zero out.

Return value

Returns a value of the DATETIME type.

If datetime is of the DATE type and fmt is set to hour, minute, or second, the time part of the returned value defaults to 00:00:00.

Examples

Example 1: Truncate the input time to the minute.

select date_trunc("minute", "2020-11-04 11:12:13");
+---------------------------------------------+
| date_trunc('minute', '2020-11-04 11:12:13') |
+---------------------------------------------+
| 2020-11-04 11:12:00                         |
+---------------------------------------------+

Example 2: Truncate the input time to the hour.

select date_trunc("hour", "2020-11-04 11:12:13");
+-------------------------------------------+
| date_trunc('hour', '2020-11-04 11:12:13') |
+-------------------------------------------+
| 2020-11-04 11:00:00                       |
+-------------------------------------------+

Example 3: Truncate the input time to the first day of a week.

select date_trunc("week", "2020-11-04 11:12:13");
+-------------------------------------------+
| date_trunc('week', '2020-11-04 11:12:13') |
+-------------------------------------------+
| 2020-11-02 00:00:00                       |
+-------------------------------------------+

Example 4: Truncate the input time to the first day of a year.

select date_trunc("year", "2020-11-04 11:12:13");
+-------------------------------------------+
| date_trunc('year', '2020-11-04 11:12:13') |
+-------------------------------------------+
| 2020-01-01 00:00:00                       |
+-------------------------------------------+

Example 5: Truncate a DATE value to the hour. 00:00:00 is returned as the time part.

select date_trunc("hour", "2020-11-04");
+----------------------------------+
| date_trunc('hour', '2020-11-04') |
+----------------------------------+
| 2020-11-04 00:00:00              |
+----------------------------------+